The invention relates to methods for sterilizing materials and preparing vaccines.
Various methods and devices exist for the sterilization, decontamination, or disinfection of biological and non-biological materials. These methods include thermal destruction (e.g., burning), heat sterilization, irradiation (e.g., ultraviolet or ionizing irradiation), gas sterilization (e.g., using ethylene oxide), photosensitization, membrane sterilization, or the use of chemical disinfectants (formaldehyde, glutaraldehyde, alcohols, mercury compounds, quaternary ammonium compounds, halogenated compounds, solvent/detergent systems, or peroxides).
Heat sterilization (e.g., autoclaving) is often used, for example, for sterilizing medical solutions prior to use in a patient. Heat sterilization typically requires heating a solution to 121.degree. C. for a minimum of 15 minutes under pressure in an autoclave, maintaining the heat and pressure conditions for a period of time sufficient to kill bacteria, fungi, and protists and inactivate viruses in the solution.
Many reusable medical articles and materials are not suitable for disinfection or sterilization in an autoclave. For example, plastic parts on medical devices, hemodialyzers, and fiber optic devices are commonly sterilized by chemical germicide treatment. In general, germicides require several hours of treatment for the inactivation of microorganisms.
To ensure sterility in pharmaceutical production, gas sterilization is often employed. However, gas sterilization (e.g., using ethylene oxide) can be time-consuming, requiring prehumidification, heating, and evacuation of a sample chamber, followed by treatment with high concentrations of the gas for up to 20 hours at a time.
When properly used, traditional disinfectants can inactivate vegetative bacteria, certain fungi, and lipophilic or medium-sized viruses. However, these disinfectants often do not arrest tubercle bacillus, spore-forming bacteria, or non-lipophilic or small-sized viruses.
Another method for lysing cells, and thereby sterilizing a sample is described in Microbiology (Davis et al., Harper & Row, Hagerstown, Md., 1980). This procedure of freezing and thawing the sample is believed to exert its effect through formation of tiny pockets of ice within the cells when a suspension of bacteria is frozen. The ice crystals and the high localized concentrations of salts both cause damage to the bacteria. A single freezing event is generally sufficient to kill only some of the bacteria, but repeated freeze-thaw cycles result in a progressive decrease in viability. Lethality is correlated with slow freezing and rapid thawing.
Traditional freeze-thaw methods are limited in the speed of the freeze-thaw cycle by the time needed to transfer heat to and from the center of the sample to effect phase changes. The equilibrium rate is particularly slow in the case of large volume samples (e.g., about 100 ml or larger). Sterilization efficiency of the traditional methods is limited by the impracticality of performing a large number of freeze-thaw cycles by those methods.
Traditional methods of food preservation include pasteurization, in which a food is held at an elevated temperature for a period of time.
There is presently a need to develop methods for inactivating microbes and viruses from protein preparations while maintaining the integrity and therapeutic value of the proteins. The development of methods for inactivation of non-encapsulated viruses is especially challenging, since the outer coats of such viruses generally include proteins similar to the proteins one wishes to retain.